RADIAL STABILITY

BACKGROUND OF THE INVENTION

HELD OF THE INVENTION

The present invention generally relates to bearing assemblies, and more particularly to bearing assemblies for video tape recorders (hereinafter referred to as VTR) for use with a rotary head device using a bearing having provision for adjusting radial stability for providing low noise and reliable rotary performance.

RELATED ART

VTR scanners use various types of bearings for rotation purposes.

Among the bearings used, fluid bearings and ball bearings are well known. In a conventional rotary head device using a fluid bearing mechanism, such a mechanism includes a rotatable shaft, a housing and a lubricant. The rotatable shaft has Herringbone patterned grooves etched onto its cylindrical surface.

The housing has a bore in which the shaft rotates, with the bore having an internal diameter slightly greater than the outer diameter of the shaft. The lubricant within the housing interfaces between the rotatable shaft and the housing. This combination provides radial rigidity for the rotary device.

However, in time, the radial rigidity would be inevitably reduced due to wear and friction.

With respect to ball bearings, a typical rotary device again includes a rotatable shaft, a housing and a lubricant. Instead of Herringbone shaped grooves, the rotatable shaft has affixed thereon an inner race having a semi- annular groove whereas the housing has a matching outer race affixed thereto, both races disposed to form an annular groove. The rotary device further includes balls retained between both races within the annular groove. The balls and the lubricant reside in the annular groove and operate to provide radial rigidity to the rotary device as the shaft rotates about its axis. However, such a structure as described above would generate radial runout for reasons such as imperfections of balls and imprecise positioning of the races.

When a rotatable shaft is no longer sufficiently rigid with respect to its surroundings, vibrational oscillations will occur in both radial and axial directions of the shaft. Such oscillations in a rotary head device would invariably result in increased level of acoustic noise and produce erratic magnetic head movement resulting in signal timing errors. Precision bearings may reduce these undesirable effects, but they are expensive to manufacture.

Therefore, it is desirable to have a bearing, inexpensive to manufacture and having a provision for adjusting radial play to thereby improve the radial rigidity to assist in minimization of noise and erratic head movement.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a bearing assembly for use in a rotary device, the assembly including a housing having a cylindrical bore configured and dimensioned for receiving therein a bushing member having an axial bore axially extending therethrough which, in turn receives a rotatable shaft therein.

The bushing member is generally cylindrically configured including a main body portion which, has an outer diameter slightly less than that of the cylindrical bore, the bushing member further including a first and a second collet axially oppositely extending from the faces of the main body portion. Each of the collets includes a set of generally identical arcuate sleeve segments with intervening slots configured to form a part of the axial bore for receiving therein the rotatable shaft. The distal end in the circumferential direction of each arcuate sleeve segment has affixed thereto a radially outwardly extending member positioned later in the rotation direction of the shaft, and further affixed thereto a generally aligned radially inwardly extending member extending into the axial bore. The set of inwardly extending members of the first collet is angularly displaced by a half of the angle of a sleeve segment relative to the other set of the second collet. With respect to an axial end view of the bushing member, radially inward ends of the radially inwardly extending members of each collet form a circle having a diameter slightly greater than that of the rotatable shaft.

The bearing assembly further includes spring-loaded adjustment means including a first and a second collar coactingly engaging the radially

outwardly extending members for urging the tips of the radially inwardly extending members into proximate relation to the rotatable shaft when inserted into the axial bore, the adjustment means includes first and second nut members threadably coupled to opposite ends of the cylindrical bore forming an enclosure within the housing for containment of a lubricant therein, which, reduces frictional loss between the radially inwardly extending members and the rotatable shaft. The adjustment means also includes a pair of spring members one of each being interposed between a nut member and a collar for axially urging the collar into abutting engagement with and toward the end of the collet, the spring members being configured and dimensioned for axial stability of the adjustment means.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an exploded perspective view of a bearing assembly in accordance with the present invention;

FIG. 2 is a cross-sectional view of a collet of the bearing assembly of FIG. 1 as viewed generally along line 2-2 thereof;

FIG. 3A is a partial cross-sectional view of a collar having a guiding surface portion riding over an arcuate sleeve segment of a collet in accordance with the present invention;

FIG.3B is a partial cross-sectional view similar to FIG. 3A showing the collar having a cam surface portion riding over an arcuate sleeve segment of the collet of FIG. 2 urging conical member tips into contact with the shaft of the assembly of FIG.;

FIG.4 is a cross-sectional view of the adjusting elements coacting with a collet for applying radial force to a shaft in accordance with the present invention; and

FIG.5 is cross sectional view of a rotary head device utilizing the bearing assembly of FIG. 1.

A better understanding of the present invention can be obtained by considering the following detailed description taken together with the

accompanying drawings which illustrate a preferred embodiment of the present invention as used in a rotary head device.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, and particularly to FIG. 1, there is shown an exploded perspective view of a bearing assembly, generally designated 10 in accordance with the present invention. The assembly 10 includes a generally rigid, generally tubular housing member 12, formed of a material, such as metal. Housing member 12 had formed therein a generally cylindrical bore 14, having a longitudinally extending central axis 16.

Configured for being received within the bore 14 is a bushing member 18, having a main body portion 38 of generally cylindrical configuration, with an outer diameter approximating that of the inner diameter of the cylindrical bore 14, the bushing member 18 being intended for fixedly positioning within the cylindrical bore 14, i.e., it is non-rotatable relative to the housing member 12. The bushing member 18, has an axial bore 19 for rotatably receiving therein a shaft 32. The bushing member 18 is seated within the cylindrical bore 14 and secured therein by suitable closure and adjusting means 21 which includes a pair of collars 20, 22, a pair of spring members such as two washer- shaped springs 24, 26 and a pair of nut members such as two threaded nuts 28 0. The rotatable shaft 32 extends longitudinally through the axial bore 19 of the bushing member 18. The nut members 28, 30 of closure and adjusting means 21, when threaded to the threaded openings 14a and 14b, respectively, serve to provide an enclosure within the housing 12 for containment of lubricant therein with the shaft 32 positioned within the axial bore 19 of bushing member 18. The bushing member 18, may be unitary in construction, formed preferably of metal, and includes first and second axially aligned oppositely disposed collets 34, 36 on opposite sides of the main body portion 38 thereof. The collets 34,36 are generally identically configured and are formed for enabling compression of the ends thereof to provide gripping of the shaft 32 within the axial bore 19 thereof. The diameter of the main body portion 38 is slightly less than the diameter of the cylindrical bore 14 whereas the diameter of shaft 32 is slightly less than that of the axial bore 19.

Other than their phase relationship (described to hereinafter), collets 34 and 36 are in mirror image relation to one other when viewed in end view. Since collets 34 and 36 are otherwise structurally identical, only collet 34 will

be described in detail with reference to Figures 1 and 2. Collet 34 is generally formed as a tubular member with longitudinally extending equiangular slots which form three arcuate sleeve segments 34a, 34b, 34c. These sleeve segments 34a, 34b, 34c are non-contiguous with slots 34d, 34e, 34f in between. Altogether, these segments and slots form a part of the axial bore 19.

To provide bearing edges for shaft rotation, each sleeve segment, such as sleeve segment 34a, is provided with a bearing tip having the position thereof controlled radially by a cam follower means, which coacts with a cam surface of the collar 20 (or 22). The bearing tip and cam follower means are in the form of a ridge or conical projection 41a (as well as 41b and 41c) and a spherical member 35a (as well as 35b and 35c), each of which is secured to a distal end of one of the segments, such as segment 34a. In the embodiment illustrated, there are three arcuate sleeve segments 34a-34c which together define a tubular opening or a part of the axial bore 19. Each of the bearing tips of the conical projections 41a-41c project radially inwardly into the bore 19. For enabling radial position adjustment of these tips, suitable cam follower means, in the form of the spherical members 35a-35c are secured to the outer surface of the segments 34a-34c, respectively, in general radial alignment with the conical projections 41a-41c, respectively. The spherical members, in turn, as will be hereinafter described, are urged inwardly by a cam surface 20a on the inner part of the cup-shaped collar 20 (or 22).

The nut members 28, 30 of the closure and adjusting means, in addition to providing housing closure, serve to provide axial adjustment of the distance between the outer faces thereof, which distance adjustment translates into simultaneous radial displacement of the tips of the conical projections 41a-41c. This translation of axial movement into radial position is effected by the nut members 28, 30 urging against the springs 24, 26 which, in turn, urge against the collars 20, 22, respectively.

Each collar, such as collar 20, is generally cup-shaped with an inner cam surface 20a which is suitably dimensioned and configured for enabling coaction with the cam follower surfaces of the spherical members 35a-35c, such as shown in Figures 3A and 3B. By reference to Figure 3A, the inner surface of the collar 20 includes the cam surface 20a and an adjacent generally cylindrical guiding surface 20b, the inner diameter of the guiding surface 20b being generally equal to, or slightly greater than, the diameter of a circle which encompasses the radially remote parts of the spherical members 35a-

35c. As the collar 20 is urged axially inwardly by tightening nut 28, the cam surface 20a is urged into engagement with the members 35a-35c, as a consequence of which, as shown in Figure 3B, the bearing tips of the conical projections 41a-41c are displaced radially inwardly into engagement with, or in proximate relation to the outer surface of the shaft 32. To facilitate the deflection of the distal end of each sleeve segment, by reference to Figure 1, there is provided a reduced diameter portion or recess 42a between the outer end of the collet 34 and the main body portion 38 of bushing member 14, this recess 42a making each of the sleeve segments 34a-34c more compliant to deflection or bending.

For optimum performance of the bearing assembly 10, there is a defined positional relationship of the bearing tips of conical projections 41a- 41c relative to each other within a set of such projections and a defined positional relationship of one set relative to the other. One set of projections 41a-41c are positioned, relative to the direction of rotation of the shaft 32, so that they are downstream, or later in the path of rotation of the shaft 32. That is, with the shaft 32 of Figure 1, rotating in the direction of the arrow 33 thereabout, a given point on the shaft 33 will pass a first end of a given sleeve segment, sans projection, after which it passes the other end with the projection. Furthermore, with respect to each set of projections on opposite sides, that is the projections of collets 34 and 36, one set of projections will be offset circumferentially from the other by an angle equal to one-half the angle of a given segment. For example, in the embodiment of Figures 1 and 2, the arc angle for a sleeve segment 34a (or 34b or 34c) is 120 degrees. Viewed axially relative to bore axis 16, the slots 34d-34f of one set are displaced by an angle of sixty degrees relative to like slots of the opposite set of collet 36.

The purpose of the angular position of the conical projections 41a-41c relative to the direction of rotation of the shaft 32 is to enable the lubricant to be forced to flow toward the tips thereof; while the reason for the angular displacement of one set of slots relative to the other sets is to provide a six point bearing support for the shaft 32, with one set of three tips offset relative to the other, to assist in establishing and maintaining radial rigidity of the shaft relative to the bearing tips.

As previously described, collets 34 and 36 are generally identical except that one is shifted by 60 degrees in phase relative to the other so to provide better radial stability. Similarly, collar 22, washer-shaped spring 26,

threaded nut 30 and collet 36 function the same as collar 20, spring 24, threaded nut 28 and collet 34. Therefore, only the former group is discussed.

Referring now to Figure 4, there is shown an alternate method of mounting of the cam follower spherical members that is a slight variant of that shown in Figures 1 and 2. In Figures 1 and 2, the spherical members 35a- 35c are mounted atop or tangential to the outer surfaces of the respective sleeve segments 34a-34c. In Figure 4, the spherical cam follower members 35a', 35b' and 35c' are fitted within recesses formed in the outer surfaces of sleeve segments 34a', 34b' and 34c'. Functionally, the two methods operate the same. Operationally, with reference to Figures 1 and 4, the shaft 32 rotates about the axis 16 within bore 19 of the bushing member 18. The ends of the housing 12 are closed by the threaded nuts 28 and 30, with the spring members 24 and 26 interposed between the inner surfaces of the nuts and the outer surfaces of the collars 20 and 22. The shaft 32 passes through aligned central apertures in the nuts 28, 30 with rotation of the shaft 32 within the assembly 10 being facilitated by lubricant 62 within the inner chamber of the thus enclosed housing, the lubricant 62 having an effective viscosity of about 1500 Pa-Sec at -40 ^* C, about 600 Pa-Sec at +25 "C, and about 4 Pa-Sec at +55 ^* C. On rotation, the lubricant 62 is carried by the outer surface of the shaft 32 toward the bearing tips of the projections 41a-41c to assist in maintaining lubrication of the shaft 32 relative to these bearing tips.

For operation purposes, radial rigidity or stability of the shaft 32 can be adjusted to compensate for wear by further adjustment of one or both of the nut members 28, 30, each of which is provided with a plurality of diametrically opposed recess in the outer surface thereof, the recess being circularly configured for receiving the tips of a spanner wrench (not shown) or other similar tool.

A preferred embodiment generally designated 50 as applied to a rotary head device is described in the following with reference to FIG. 5. A rotatable shaft 32 is pressed in and secured in place at the central portion of a stationary member 65 which includes a housing 12, one of its free ends being securely seated on a thrusting bearing 70, the other end having a rotatable member 75 rigidly affixed thereto. At least one rotary magnetic head 77 is mounted on the rotatable member 75. Also mounted on the rotatable member 75 is a rotary transformer 79 on the rotary side of the rotary head device for transmitting to the stationary side an electrical signal extracted from a

magnetic tape (not shown) through at least the magnetic head 77. On the other hand, mounted on the stationary member 65 is a rotary transformer 81 on the stationary side of the rotary head device which receives the aforementioned electric signal. Also proximal to the stationary member 65, there is secured a motor 83 used for rotating the shaft 60. The stationary member 65 having a cylindrical bore 14 which in combination with two nut members 28, 30 threadably coupled to form an enclosure within which a bearing assembly is located. Because its detailed configuration and operations have been described elsewhere in the specification, shown and explained in the FIG. 5 is only a part of the bearing assembly which includes a bushing member 18 having a main body portion 38, the bushing 18 being axially bored for receiving therein the shaft 32. The bushing member 18 includes a collet having a set three of arcuate sleeve segments (not shown), one of which, segment 34a includes a neck portion associated therewith and a radially outwardly extending cam follower member 35a fixedly mounted thereon. The sleeve segment 34a further includes a radially inwardly extending member (not shown) which is operably urged by adjustment means into a proximal relation to the shaft 32. The adjustment means 21 includes a threaded nut 28 threadably coupled to the housing 12, a collar 20 including an inner cam surface (not shown) for controlling the cam follower member 35a thereby urging and bending the sleeve segment 34a (also 34b and 34c but not shown) towards the shaft 32, and the adjustment means 21 further includes a spring 24 interposed between the threaded nut 28 and the collar 20 providing axial stability for the adjustment means. The bearing further includes a lubricant (not shown) interfacing between the bearing and the shaft 32. The shaft 32 rotates in such a way so that as the motor 83 is energized, the lubricant concentrates near the sleeve conical tip-shaft contacts or thereabout.